Showing papers on "Heck reaction published in 2021"

A Practice of Reticular Chemistry: Construction of a Robust Mesoporous Palladium Metal-Organic Framework via Metal Metathesis.

Abstract: Constructing stable palladium(II)-based metal-organic frameworks (MOFs) would unlock more opportunities for MOF chemistry, particularly toward applications in catalysis. However, their availability is limited by synthetic challenges due to the inertness of the Pd-ligand coordination bond, as well as the strong tendency of the Pd(II) source to be reduced under typical solvothermal conditions. Under the guidance of reticular chemistry, herein, we present the first example of an azolate Pd-MOF, BUT-33(Pd), obtained via a deuterated solvent-assisted metal metathesis. BUT-33(Pd) retains the underlying sodalite network and mesoporosity of the template BUT-33(Ni) and shows excellent chemical stability (resistance to an 8 M NaOH aqueous solution). With rich Pd(II) sites in the atomically precise distribution, it also demonstrates good performances as a heterogeneous Pd(II) catalyst in a wide application scope, including Suzuki/Heck coupling reactions and photocatalytic CO2 reduction to CH4. This work highlights a feasible approach to reticularly construct noble metal based MOFs via metal metathesis, in which various merits, including high chemical stability, large pores, and tunable functions, have been integrated for addressing challenging tasks.

Pd-catalyzed formal Mizoroki–Heck coupling of unactivated alkyl chlorides

Abstract: The use of alkyl chlorides in Pd-catalyzed Mizoroki-Heck coupling reactions remains an unsolved problem despite their significant potential for synthetic utility and applicability. The combination of the high thermodynamic barrier of alkyl chloride activation and kinetic propensity of alkylpalladium complexes to undergo undesired β-hydride elimination provides significant challenges. Herein, a variety of alkyl chlorides, even tertiary chlorides, are shown to efficiently participate in Mizoroki-Heck cross-coupling reactions with excellent functional group compatibility under mild reaction conditions via photoinduced Pd catalysis. The reaction is applied to late-stage functionalizations of diverse biologically significant scaffolds and iterative double Mizoroki-Heck annulations, affording high molecular complexity in a single step. Notably, studies on the kinetic isotope effects in combination with density functional theory (DFT)-computations completely exclude the involvement of a previously proposed β-hydride elimination in the catalytic cycle, revealing that the chlorine atom transfer process is the key catalytic turnover step. This distinctive single-electron transfer mediated reaction pathway resolves a longstanding challenge in traditional two-electron based Pd-catalyzed Mizoroki-Heck cross-coupling with alkyl electrophiles, wherein the β-hydride elimination is involved in the formation of both the desired product and undesired by-products.

Visible Light-Induced Pd-Catalyzed Alkyl-Heck Reaction of Oximes

Abstract: A visible light-induced palladium-catalyzed oxidative C–H alkylation of oximes has been developed. This mild protocol allows for an efficient atom economical C–C bond construction of alkyl-substitu...

Enantioselective Intermolecular Heck and Reductive Heck Reactions of Aryl Triflates, Mesylates, and Tosylates Catalyzed by Nickel.

Abstract: Nickel-catalyzed intermolecular Heck reaction of cycloalkenes proceeds well with aryl triflates, mesylates and tosylates in excellent enantiomeric ratios. The asymmetric reductive Heck reaction also works with a 2-cyclopentenone ketal, which is equivalent to conjugate arylation of the enone itself.

Olefin functionalization/isomerization enables stereoselective alkene synthesis

Abstract: Despite tremendous efforts aimed at devising methods for stereoselective alkene synthesis, critical challenges are yet to be addressed. Direct access to a diverse range of 1-aryl(boryl)-1-methyl-functionalized tri- and tetrasubstituted trans alkenes, entities that are prevalent in many important molecules, through a catalytic manifold from readily available α-olefin substrates remains elusive. Here, we demonstrate that catalytic amounts of a non-precious N-heterocyclic carbene–Ni(I) complex in conjunction with a sterically bulky base promote site- and trans-selective union of monosubstituted olefins with a wide array of electrophilic reagents to deliver tri- and tetrasubstituted alkenes in up to 92% yield and >98% regio- and stereoselectivity. The protocol is amenable to the preparation of carbon- and heteroatom-substituted C=C bonds, providing distinct advantages over existing transformations. Utility is highlighted through concise stereoselective synthesis of biologically active compounds. Stereoselective synthesis of tri-and tetrasubstituted olefins is challenging due to the usually low energy difference between their E/Z isomers. Now, access to these molecules in high E:Z ratios from monosubstituted olefins is achieved through a sequential nickel-catalysed Heck reaction and alkene migration.

Total Synthesis of Anti-Cancer Meroterpenoids Dysideanone B and Dysiherbol A and Structural Reassignment of Dysiherbol A

Abstract: The first total synthesis of marine anti-cancer meroterpenoids dysideanone B and dysiherbol A have been accomplished in a divergent way. The synthetic route features: 1) a site and stereoselective α -position alkylation of Wieland-Miescher ketone derivative with a bulky benzyl bromide to join the terpene and aromatic moieties together and set the stage for subsequent cyclization reactions; 2) an intramolecular radical cyclization to construct the 6/6/6/6-tetracycle of dysideanone B and an intramolecular Heck reaction to forge the 6/6/5/6-fused core structure of dysiherbol A, respectively. A late-stage introduction of the ethoxy group in dysideanone B reveals that this group might come from the solvent ethanol. The structure of dysiherbol A has been revised based on our chemical total synthesis.

Enantioselective CO2 Fixation Via a Heck-Coupling/Carboxylation Cascade Catalyzed by Nickel.

Abstract: A novel asymmetric nickel-based procedure has been developed in which CO2 fixation is achieved as a second step of a truncated Heck coupling. For this, a new chiral ligand has been prepared and shown to achieve enantiomeric excesses up to 99 %. The overall process efficiently furnishes chiral 2,3-dihydrobenzofuran-3-ylacetic acids, an important class of bioactive products, from easy to prepare starting materials. A combined experimental and computational effort revealed the key steps of the catalytic cycle and suggested the unexpected participation of Ni(I) species in the coupling event.

Nickel Nanocatalysis: An Efficient Tool for Heck Reaction

Abstract: Of late, developing non‐precious catalytic protocol with high performance is of primary significance and furnishes fascinating sets of results for synthetic chemists. This minireview describes the advances and scopes of nickel nanoparticles being employed as catalysts in Heck cross‐coupling reactions of aryl halides and olefins in 21st century. We have focused on the methods of preparation of nanocatalysts and emphasized on different techniques employed in the generation of nickel nanoparticles or bimetallic alloy nanoparticles.

Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

Abstract: Herein we report a palladium-catalyzed [2 + 2 + 1] annulation among 3-iodochromones, bridged olefins, and cyclopropenone, giving a variety of chromone fused cyclopentanones that are of interest in medicinal chemistry. This protocol involves a Heck coupling/C(sp2)–H activation/carbonylation sequence, forming two C(sp2)–C(sp3) bonds and a C(sp2)–C(sp2) bond as well as a cyclopentanone unit in a single operation. Importantly, cyclopropenone in this methodology was utilized for the first time as the sole CO surrogate in the carbonylation process; its exceptional potential in carbonylation will be an inspiration for organic chemists.

In situ construction of phenanthroline-based cationic radical porous hybrid polymers for metal-free heterogeneous catalysis

Abstract: Rational design of multifunctional radical porous polymers with redox activity for targeted metal-free heterogeneous catalysis is an important research topic. In this work, we reported a new class of phenanthroline-based cationic radical porous hybrid polymers (Phen˙+-PHPs), which were constructed from the Heck reaction between a newly designed dibromo-substituted phenanthroline ionic monomer (iDBPhen) and a rigid building block, octavinylsilsesquioxane (VPOSS). For the first time, the stable phenanthroline-based radical cation was unexpectedly discovered in these polyhedral oligomeric silsesquioxane (POSS)-based porous hybrid polymers, probably undergoing in situ reduction of the dicationic monomer iDBPhen during the alkaline reagent K2CO3-involved Heck reaction. The radical characters of the typical porous polymers Phen˙+-PHP-2 and Phen˙+-PHP-2Br were confirmed from the electron paramagnetic resonance (EPR) spectra and X-ray photoelectron spectra (XPS). The chemical structures and porous geometry were fully characterized by a series of advanced technologies. Surprisingly, the metal-free cationic radical polymer Phen˙+-PHP-2 exhibited high heterogeneous catalytic efficiency in the H2O2-mediated selective oxidation of various sulfides to sulfoxides with high yields under mild conditions, owing to the electron-accepting and redox ability of Phen-based dications and radical cations. Moreover, the extended sample Phen˙+-PHP-2Br prepared by post-treatment of Phen˙+-PHP-2 with aqueous HBr was also employed as a metal-free efficient heterogeneous catalyst in the conversion of CO2 with epoxides into cyclic carbonates under atmospheric pressure and low temperatures. The remarkable catalytic performance in CO2 conversion should be assigned to the synergistic catalysis of POSS-derived Si–OH groups and nucleophilic Br− anions and N active atom-involved Phen cationic radical moieties within Phen˙+-PHP-2Br. These two catalysts can be facilely recovered and reused, also with stable recyclability in the above catalytic reaction systems, achieving the heterogeneous catalytic demands for multipurpose reactions.

Phenanthroline functionalized polyacrylonitrile fiber with Pd(0) nanoparticles as a highly active catalyst for the Heck reaction

Abstract: A series of polyacrylonitrile fibers (PANF) functionalized with nitrogen-containing ligands were prepared and then used to synthesize fiber-supported Pd(0) nanoparticle catalysts The phenanthroline-functionalized PANF with immobilized Pd(0) nanoparticles (PANPhenF-Pd(0)) had the best catalytic activity for the Heck reaction under solvent-free conditions The PANPhenF-Pd(0) efficiently stabilized the nanoparticles and they were well-dispersed with Pd(0) particle sizes of about 3 nm The PANPhenF-Pd(0) structure was further characterized by a variety of instrumental methods A probable mechanism based on the fiber's microenvironment is proposed for the Heck reaction catalyzed by PANPhenF-Pd(0) The PANPhenF-Pd(0) catalyst is easily recovered from the reaction system and can be used up to six times with only a slight decrease in catalytic activity and with low Pd leaching The PANPhenF-Pd(0) catalyst also has excellent catalytic activity for gram-scale use

Recent Developments in Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles

Abstract: The Mizoroki–Heck reaction is considered as one of the most ingenious and widely used methods for constructing C–C bonds. This reaction mainly focuses on activated olefins (styrenes, acrylates, or vinyl ethers) and aryl/vinyl (pseudo) halides. In comparison, the studies on unactivated alkenes and alkyl electrophiles are far less due to the low reactivity, poor selectivity, as well as competitive β-H elimination. In the past years, a growing interest has thus been devoted and significant breakthroughs have been achieved in the employment of unactivated alkenes and alkyl electrophiles as the reaction components, and this type of coupling is called as Heck-type or Heck-like reaction, which distinguishes from the traditional Heck reaction. Herein, we give a brief summary on Heck-type reaction between unactivated alkenes and alkyl electrophlies, covering its initial work, recent advancements, and mechanistic discussions. 1 Introduction 2 Intramolecular Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles 2.1 Cobalt-Catalyzed Intramolecular Heck-Type Reaction 2.2 Palladium-Catalyzed Intramolecular Heck-Type Reaction 2.3 Nickel-Catalyzed Intramolecular Heck-Type Reaction 2.4 Photocatalysis and Multimetallic Protocol for Intramolecular Heck-Type Reaction 3 Intermolecular Heck-Type Reaction of Unactivated Alkenes and Alkyl Electrophiles 3.1 Electrophilic Trifluoromethylating Reagent as Reaction Partners 3.2 Alkyl Electrophiles as Reaction Partners 4 Oxidative Heck-Type Reaction of Unactivated Alkenes and Alkyl Radicals 5 Conclusions and Outlook

Organosulfur, organoselenium, and organotellurium ligands in the development of palladium, nickel, and copper-based catalytic systems for Heck coupling

Abstract: During the last two decades, several research groups across the globe have utilized organochalcogen compounds as: (i) ligands for developing homogeneous, i.e. chalcogen-ligated metal complexes, and heterogeneous catalytic systems; (ii) stabilizers for developing metal nanocatalytic systems (iii) building blocks of single-source precursors for nanosized metal chalcogenides. The electron-donating abilities of chalcogen (S, Se, and Te) donors make them promising in the field of phosphine-free catalysis. Generally, such ligands and catalytic systems are easily synthesizable. In the preceding decade (2011–2020), a variety of homogeneous, heterogeneous, and nanocatalytic systems have been developed using organosulfur, organoselenium, and organotellurium ligands. Such catalytic systems have been extensively used for the Heck coupling reaction. This perspective article covers the synthetic methodologies used for such ligands and catalytic systems designed during 2012–2020. Another major focus of this article is the catalysis of Heck coupling with such systems. The substrate scope, green catalysis, use of conventional and non-conventional sources of energy, and catalytic performances are analysed and covered. The effects of the operational parameters of reactions have also been discussed. Various factors that influence the catalytic efficiencies have been highlighted, and the variations in the catalytic efficiencies of different catalytic systems have been critically analysed. The behaviours of the catalytic systems during the reactions have been summarized and correlated with mechanistic pathways. The catalytic cycles proposed for this reaction have also been paid sufficient attention.

Aziridine used as a vinylidene unit in palladium-catalyzed [2 + 2 + 1] domino annulation

Abstract: A novel palladium-catalyzed three-component reaction of 3-iodochromones with bridged olefins and aziridine is described, which employs a [2 + 2 + 1] domino annulation strategy to produce chromone fused methylenecyclopentanes in moderate to good yields via a Heck coupling/C(sp2)–H activation/imine–enamine tautomerization/retro-aza-Michael addition sequence. Significantly, aziridine was used as a vinylidene unit by cleavage of two C–N bonds and was successfully introduced into the products for the first time.

Construction of Indoline/Indolenine Ring Systems by a Palladium-Catalyzed Intramolecular Dearomative Heck Reaction and the Subsequent Aza-semipinacol Rearrangement.

Abstract: The palladium-catalyzed intramolecular dearomative Heck reaction of 2,3-disubstituted indoles serves as an access to spiro-indoline products Herein, we report an efficient construction of indoline

Biogenic synthesis of Pd-nanoparticles using Areca Nut Husk Extract: a greener approach to access α-keto imides and stilbenes

Abstract: An eco-friendly green method for a one-step synthesis of palladium nanoparticles and their synthetic utility are reported. Phytochemicals like amines, alcohols, and phenols present in the Areca Nut Husk extract facilitate the reduction of Pd(II) to Pd(0). The phytochemicals serve as stabilising agents and ligands for palladium reduction and the need for an external ligand is avoided. The Field Emission Scanning Electron Microscopy and Transmission Electron Microscopy of newly synthesized palladium nanoparticles revealed a spherical morphology. The catalytic activity of the nanoparticles was tested for 1,2-difunctionalization of ynamides, Heck coupling, denitrogenative coupling of phenylhydrazine and C–H arylation of indole. Moreover, catalyst recyclability, control experiments, mechanistic elucidation, and gram-scale synthesis are elaborated.

Pd-catalyzed enantioselective intramolecular Heck reaction to access disubstituted dihydroisoquinolinone with a terminal olefin

Abstract: A first palladium-catalyzed asymmetric intramolecular Heck reaction for the construction 3, 4-dihydro-1-(2H)-isoquinolinone containing the quaternary carbon chiral center has been developed. The salient features of this reaction include high efficiency, high enantioselectivity, the novel chiral ligand and diverse transformations.

Visible Light Induced Brønsted Acid Assisted Pd-Catalyzed Alkyl Heck Reaction of Diazo Compounds and N-Tosylhydrazones

Abstract: A mild visible light-induced palladium-catalyzed alkyl Heck reaction of diazo compounds and N -tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Bronsted acid-assisted generation of hybrid palladium C(sp 3 )-centered radical intermediate, which allowed for new selective C-H functionalization protocol.